At present, there are a lot of hydrocarbon conversion processes using solid acid catalysts at low temperatures, such as alkylation (alkylation of an isoalkane with an olefin, and alkylation of benzene with an olefin), isomerization (isomerization of C4, C5 and C6 low-carbon n-alkanes, and isomerization of low-carbon olefins), olefin oligomerization, hydroisomerization and the like. These low temperature hydrocarbon conversion processes require solid acid catalysts having strong acidity, such as supported heteropoly acid catalysts, supported heteropoly acid salt catalysts, zeolite-molecular, sieve catalysts, SO42−/oxide super acid catalysts, supported Brönsted-Lewis conjugated solid super acid catalysts, solid polymerization ion exchange resins and oxide or molecular sieve catalysts treated with Brönsted acids or Lewis acids. These solid acid catalysts participate in hydrocarbon conversion reactions according to the reaction mechanism of carbenium ions.
The above-mentioned alkylation of an isoalkane with an olefin refer to the reactions of C4-C6 isoalkanes with C3-C6 monoolefins to produce isomerized long-chain alkanes. An example of the products of the alkylation is C8 isooctane produced in the reaction of isobutane with butene, which has a high octane number and a low Reid vapor pressure, and is useful as an excellent additional component for gasoline.
Here, the industrially used catalyst of the above-mentioned alkylation processes is H2SO4 or HF, which has a concentration of about 95%. H2SO4 alkylation processes carried out at a low temperature (about 10° C.) can prevent olefins from building-up reactions, but they will produce a big amount of waste acids, which cannot be recycled and will pollute the environment seriously if discharged. HF alkylation processes are carried out at a low temperature (generally between 20 and 40° C.), too, but HF is easily volatile and can easily cause environmental pollution and harm the production environment. The industrial use of H2SO4 and HF for the production of alkylate oils has lasted for several decades, and “Alkylation of isobutane with C4 olefins”, Ind. Eng. Chem. Res., 27, 381-379 (1988), Handbook of Petroleum Refining Processes, 1, 23-28 (1986) and Oil Refining Technology in China, China Petrochemical Press, 206-217 (1991) contain detailed discussions about it.
Since H2SO4 and HF as strong liquid acids pollute the environment seriously, it has become an important research subject for the researchers in the international catalyst field to use solid acids to replace them as alkylation catalysts. Recently, various solid acid catalysts used in the above-mentioned alkylation processes are reported, such as the SO42−/oxide super acidic catalysts disclosed in JP01,245,853, U.S. Pat. No. 3,962,133, U.S. Pat. No. 4,116,880, GB1,432,720 and GB1,389,237; the CF3SO3H/silica catalyst disclosed in U.S. Pat. No. 5,220,095, U.S. Pat. No. 5,731,256, U.S. Pat. No. 5,489,729, U.S. Pat. No. 5,364,976, U.S. Pat. No. 5,288,685 and EP0,714,871; the Pt-AlCl3-KCl/Al2O3 catalyst disclosed in U.S. Pat. No. 5,391,527 and U.S. Pat. No. 5,739,074; the Lewis acid supported catalysts, such as SbF5, BF3 and AlCl3 supported catalysts, disclosed in U.S. Pat. No. 5,157,196, U.S. Pat. No. 5,190,904, U.S. Pat. No. 5,346,676, U.S. Pat. No. 5,221,777, U.S. Pat. No. 5,120,897, U.S. Pat. No. 5,245,101, U.S. Pat. No. 5,012,033, U.S. Pat. No. 5,157,197, CN1,062,307A and WO95/26,815; the supported heteropoly acid catalysts disclosed in CN1,184,797A, CN1,232,814A, U.S. Pat. No. 5,324,881 and U.S. Pat. No. 5,475,178; the molecular sieve catalysts disclosed in U.S. Pat. No. 3,549,557, U.S. Pat. No. 3,644,565, U.S. Pat. No. 3,647,916, U.S. Pat. No. 3,917,738 and U.S. Pat. No. 4,384,161.
WO94/03415 discloses a process for alkylation of an alkane with an olefin, comprising contacting an olefin-containing feed with an isoalkane-containing feed in the presence of crystalline microporous materials, under alkylating conditions including temperatures at least equal to the critical temperature of the principal components and pressures at least equal to the critical pressure of the principal component of the feed. The crystalline microporous materials include various zeolites and layered materials, wherein the zeolites include ZSM zeolites, offretitite zeolite, MCM zeolites, mordenite, REY zeolite etc., and the layered materials include layered silicates and clays etc. When a MCM zeolite is used as the catalyst, said process has an increased butene conversion and an improved catalyst activity stability. However, the olefin conversion in said process is still low, which is only 86.0 to 99.4% by weight.
CN1,125,639A discloses a process for alkylation of isobutane with an olefin, comprising preparing a catalyst by dissolving 10 to 70% of heteropoly acids including PW12, PMo12, SiW12, PW12Mo12-n (n=1-11) etc. in a solvent selected from low-carbon fatty acids, esters, ketones, ethers, alcohols or mixtures of fatty acids and fatty alcohols, to catalyze the alkylation of isobutane with butene, wherein the reaction is carried out at a temperature of 10 to 70° C., and the alkane/olefin ratio is 1.5 to 18. Although said process prevents the equipment from being severely eroded by H2SO4 and HF catalyst, the problem of isolation of the reaction product from the solvent appears, for the reaction is carried out in a liquid phase. Moreover, said process for alkylation of isobutane with butene has a relatively low olefin conversion and a relatively low alkylate oil yield. For example, according to Examples 1-9, the alkylate oil yield was only 0.693 to 1.736 (relative to the weight of the olefin) in the alkylation performed in a batch reactor.
CN1,125,640A discloses a process for alkylation of isobutane with butene, wherein the alkali salt or ammonium salt of a heteropoly acid selected from phospho-tungstic acid, phospho-molybdic acid, silico-tungstic acid and silico-molybdic acid is used as the catalyst, the varying range (g/molecule) of the alkali metal and the ammonium ion is 0.5 to 3.0 for the phosphor series and 0.5 to 4.0 for the silicon series, the alkylation temperature is 30° C., and the alkane/olefin ratio is 15:1. Said process for alkylation of isobutane with butene still has a relatively low alkylate oil yield, and fails to retain catalyst activity stability. For example, according to the Examples, the alkylate oil yield was at most 1.845, relatively to the weight of the olefin, in the alkylation of isobutane with butene performed in a batch reactor, and the catalytic activity decreased rapidly as the reaction times increased. For example, according to Example 1, Cs2.5H0.5PW12 was used as the catalyst, 0.4378 g olefin and an alkane at an alkane/olefin ratio of 15 were added in the reactor, the reaction lasted for 2 hours at 30° C. to produce 0.8118 g alkylate oil, the alkylate oil yield was 1.854, the catalyst was isolated, and used again under the same conditions after dried for 2 hours at 100° C., and the alkylate oil yield was 1.384.
U.S. Pat. No. 5,324,881 discloses a process for alkylation of an isoalkane with an olefin, comprising reacting an isoalkane with an olefin in the presence of a supported heteropoly acid catalyst, under alkylating conditions, thus to obtain an alkylate. The heteropoly acid comprises, as the central element/elements, at least one element selected from the group consisting of P, Si, B, Ge, As, Se, Ti, Zr, Mn, F, V, Ce and Th, and, as the coordinating element/elements, at least one element selected from the group consisting of Mo, W, V, Mn, Co, Ni, Cu, Zn and Fe. According to the examples, all the heteropoly acid catalysts were treated at a temperature above 350° C., the olefin conversion was at most 87% by weight, and the C5+ alkylate oil yield was at most 1.4 g/g C4+. The tests prove that said process does not have a satisfactory catalyst activity stability. CN1,232,814A discloses a process for alkylation of a low-carbon isoalkane with an olefin, in which a supported heteropoly acid catalyst is used, the reaction is carried out at a temperature at least equal to the critical temperature of the isoalkane and a pressure at least equal to the critical pressure of the isoalkane. Said process has the advantages of a high olefin conversion and a high alkylate oil yield, as well as improved catalyst activity stability.
CN1,246,467A discloses a process for alkylation of a low-carbon isoalkane with an olefin, characterized in that the catalyst as used consists of 40 to 95% by weight of a porous inorganic support, and 1 to 60% by weight of a Brönsted acid and 0.3 to 15% by weight of a Lewis acid supported on the porous inorganic support, wherein the Brönsted acid is a heteropoly acid or inorganic mineral acid, and the Lewis acid is selected from AlCl3, BF3 or XF5, wherein X is P, As, Sb or Bi. In said process, the active component of the catalyst does not flow away easily, and the conversion and selectivity of the reaction are both relatively high.
CN1,331,065A discloses a process for alkylation of an isoalkane with an olefin over the catalysis of a solid acid, characterized in that the alkylation is carried out by contacting, as the reaction material, a mixture of C4-C6 isoalkane, C3-C6 monoolefin and 10 to 3000 ppm a compound containing a strongly electronegative element as promoter with a solid acid catalyst. The conversion and selectivity of the reaction are both relatively high, and stability of the catalyst is satisfactory.